1. Field of the Invention
The present invention relates to automated systems and methods for processing samples, such as biological samples. Particular exemplary embodiments relate to removing supernatant from sample vials using vision-guided aspiration apparatus and methods.
2. Description of the Related Art
Automated sample processing systems may include a variety of devices and subsystems intended to perform a number of different processing steps on the samples being processed. In many instances, devices are provided to remove liquid from a sample container. Pipettors and aspirators, which use suction to remove liquids, are commonly used for this purpose. In some cases, such as in U.S. application Ser. No. 13/657,633 entitled “Automated Pelletized Sample Decanting Apparatus and Methods,” which is incorporated herein by reference, liquid may be removed by overturning the container to decant the liquid. In other cases, the sample container may include a permeable or openable bottom surface that allows liquid to elute or drain out of the container.
While many different kinds of existing liquid removing systems are used, such systems may have certain limitations or drawbacks. In particular, when the liquid to be removed is a supernatant that is in the same container as a solid or pelletized sample, in some cases it may be difficult or impossible to use a conventional device to accurately remove the supernatant without disturbing or removing the sample, and in such cases it may be necessary to remove the supernatant manually, which can be time-consuming and relatively expensive. Furthermore, devices that can remove supernatant without disturbing the sample may only be able to do so when the sample is accurately positioned at a particular location, or when the sample has particular dimensions or other properties. For example, a pipettor that is programmed to descend to a predetermined height to aspirate supernatant may operate well when the pellet is one size, but leave surplus supernatant in the container if the pellet is smaller than expected, or aspirate some or all of the pellet if the pellet is larger than expected. As another example, devices that decant the liquid may operate effectively and accurately regardless of the pellet size, but may require a relatively large space commitment and include multiple relatively complex moving parts.
The foregoing problems may exist in a variety of processing systems. As one example, processing systems that are intended to perform steps of the QIAGEN Hybrid Capture® 2 (“HC2”) nucleic acid hybridization assay may need to remove supernatant from a pelletized sample. In the HC2 protocol, the sample may be provided in vials containing either the PreservCyt® preservative fluid (available from QIAGEN Gaithersburg, Inc. of Gaithersburg, Md.), the SurePath™ preservative fluid (available from Becton, Dickinson and Company of Franklin Lakes, N.J.), or other fluids. In the HC2 process, the sample may be mixed and aliquoted to a sample processing container, such as a 10 milliliter Sarstedt conical tube or a 15 milliliter VWR or Corning brand conical tube, or an automated processing tube strip. Sample conversion buffer (e.g., 0.4 milliliters added to 4.0 milliliters of specimen for 1-2 tests per sample) is added to the processing tube, and then the tube is capped and thoroughly mixed using a vortex mixer with a cup attachment. Next, the tube is centrifuged in a swinging bucket rotor at 2,900 (±150)×g for 15 (±2) minutes, to form a sample pellet. In the manual process, the operator visually verifies that there is a pellet in the tube. If there is a pellet, the operator manually decants the supernatant by inverting the tube and gently blotting (approximately 6 times) on absorbent low-lint paper towels until liquid no longer drips from the tube. Each blot is done on a clean area of the towel. During blotting, the operator observes the tube to ensure that the cell pellet does not slide down the tube. Details and other processing steps of the HC2 protocol (both in manual and automated form) are provided in U.S. application Ser. No. 13/657,633.
To automate the HC2 protocol, it is necessary to separate the supernatant from the pelletized sample. U.S. application Ser. No. 13/657,633 provides a decanting system to perform this task, but alternative solutions may be desirable for a variety of reasons. Similarly, it may be desirable to provide alternative mechanisms and procedures for other processes that require a liquid to be removed from a solid sample, and particularly a pelletized sample.